Download Effect of soil humidity and pH on common scab severity – controlled

Johansen, T.J. et al / Bioforsk FOKUS 6(10)
Effect of soil humidity and pH on common
scab severity – controlled climate experiments
T.J. Johansen1, M.W. Dees2,3 & A. Hermansen2
1
Bioforsk, Norwegian Institute for Agricultural and Environmental Research, Arctic Agriculture and Land Use Division, Tromsø,
Norway 2 Bioforsk, Norwegian Institute for Agricultural and Environmental Research, Plant Health and Plant Protection Division,
Ås, Norway 3 Norwegian University of Life Sciences, Department of Plant and Environmental Sciences, Ås, Norway
[email protected]
The current study aimed at finding how soil humidity
and pH affected the severity of two common scab
pathogen species (Streptomyces turgidiscabies and
S. europaeiscabiei) in potatoes. The work was performed in the growth seasons of 2009-2011 in climate
chambers at the University of Tromsø, northern
Norway (69º 40’N). The chambers had natural light
conditions and a temperature of 18 ºC in 2009 and
18/12 ºC (day/night) in 2010-2011. The standard soil
had a pH of 4.8, and a high level (pH 7.2) was
attained by adding limestone meal. Plants of the susceptible potato cv. Gullauge, were grown in 12 litre
pots filled with a mixture of soil, fertilizer, lime and
inoculum of the two Streptomyces species produced
at Bioforsk Plant Health and Plant Protection
Division. Soil humidity was altered during a four
weeks period from the beginning of tuber formation
by keeping pots at three humidity levels (dry, normal
and wet). The water content was measured to 8, 15
and 22 percent, respectively, during this period. At
harvest the coverage of scab lesions on tubers (% of
the tubers surface area) was graded visually using an
assessment key. In addition, several yield parameters
were registered.
The results varied between years. In 2009, only
plants inoculated with S. turgidiscabies showed
significant damage (32 % coverage of tuber lesions)
compared to control plants (0 %). Tubers inoculated
with S. europaeiscabiei showed only minor damage
(7 %) this year. The scab severity was not affected by
soil humidity for any of the two Streptomyces species. In 2010, the two common scab pathogen species
showed similar damage and similar reactions to
humidity. There were significantly less scab lesions on
tubers at normal and wet conditions (19 and 13 %
coverage, respectively) than at dry conditions (35 %).
In 2011, S. europaeiscabiei caused more severe
damage on tubers than S. turgidiscabies (18 and 11 %
lesions, respectively) and there were significantly
less scab lesions at wet conditions (9 %) as compared
to dry and normal conditions (19 and 16 %, respectively).
The yields were not affected significantly by inoculation with any of the species, except for 2009 when
S. turgidiscabies reduced total yield with 20 percent.
In conclusion it seems like the common scab damage
caused by both S. turgidiscabies and S. europaeiscabiei may be reduced by wet soil conditions during
the period of tuber formation. The two pH levels did
not affect scab severity significantly in any of the
two years of experiments (studied only in 20102011).
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